Methods and apparatuses for reference signals in 2 sub-carrier pi/2 binary phase shift keying communication

ABSTRACT

The present invention provides methods and apparatuses for implementation of cyclic prefix (CP) and demodulation reference signal (DMRS) in 2 sub-carrier pi/2 binary phase shift keying (BPSK) modulation in a communication system. DMRS symbols arc interleaved with data-carrying symbols and configured such that they are alternatingly transmitted on different ones of the two sub-carriers. When a DMRS symbol is transmitted on one sub-carrier, the other sub-carrier may be unused. In implementing CP, phase rotations may be applied to modulation symbols, such that each concurrently transmitted pair of symbols is subjected to a same phase rotation. The phase rotation can be derived based on an average frequency of the two (e.g. adjacent) sub-carriers in use. The phase rotations can be updated recursively, and the update multiplied by a scaling factor.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from U.S. Provisional PatentApplication No. 62/617,878, filed on Jan. 16, 2018, and which isincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention pertains to the field of telecommunication and inparticular to methods and apparatuses for implementation of demodulationreference signals (DMRS), phase rotation with regard to cyclic prefixes(CP), or both, in 2 sub-carrier Pi/2 binary phase shift keying (BPSK)modulation in a communication system.

BACKGROUND

For enhanced Machine-Type Communication (eMTC) technologies underconsideration by the 3^(rd) Generation Partnership Project (3GPP), a 2sub-carrier Pi/2 binary phase shift keying (BPSK) signaling mechanismhas been agreed upon for eMTC 3GPP Release 15.

Pi/2 BPSK refers to a variation of BPSK modulation in which twodifferent BPSK symbol constellations are alternatingly used to modulatedata. The second constellation can be derived by rotating the firstconstellation by Pi/2 radians. 2 sub-carrier Pi/2 BPSK refers to anapproach in which two different sub-carriers (e.g. out of a possible 12sub-carriers in an LTE physical resource block) are used to transmit thedata prepared in part using Pi/2 BPSK. Data is thus transmitted via onlytwo out of the twelve subcarriers at a time. An input data stream can bemultiplexed into two streams, which are processed together to drive thetwo sub-carriers.

To support technologies such as eMTC, there is a need for methods andapparatuses for further developments in the implementation of such 2sub-carrier Pi/2 binary phase shift keying (BPSK) modulation in acommunication system.

This background information is provided to reveal information believedby the applicant to be of possible relevance to the present invention.No admission is necessarily intended, nor should be construed, that anyof the preceding information constitutes prior art against the presentinvention.

SUMMARY

An object of the present invention is to provide methods and apparatusesfor implementation of cyclic prefixes (CP), demodulation referencesignals (DMRS), or both, in 2 sub-carrier Pi/2 binary phase shift keying(BPSK) modulation in a communication system. Such aspects may beperformed for example by a mobile device (UE) for wireless uplinkcommunication in an implementation of a communication protocol such asLTE.

In accordance with an aspect of the present invention, there is provideda method for implementing demodulation reference signal symbols in 2sub-carrier Pi/2 binary phase shift keying modulation in a communicationsystem, the method comprising inserting DMRS data before Pi/2 BPSKmodulation. In accordance with another aspect of the present invention,there is provided a method for implementing a demodulation referencesignal in 2 sub-carrier Pi/2 binary phase shift keying modulation in acommunication system, the method comprising inserting DMRS pi/2 BSPKmodulated symbols before FFT and phase rotation of data. In accordancewith another aspect of the present invention, there is provided a methodfor implementing a demodulation reference signals in 2 sub-carrier Pi/2binary phase shift keying modulation in a communication system, themethod comprising inserting DMRS pi/2 BSPK modulated symbols after FFTand before phase rotation of data.

In accordance with an aspect of the present invention, there is provideda method for including a plurality of demodulation reference signal(DMRS) symbols in a physical resource block format in a communicationsystem, the method comprising: converting input data into modulationsymbols, the converting comprising performing Pi/2 binary phase shiftkeying (BPSK) modulation on the input data; and transmitting acombination of the modulation symbols and the plurality of DMRS symbolsusing a pair of sub-carriers of the physical resource block format,wherein subsequent ones of the plurality of DMRS symbols arealternatingly transmitted on different ones of the pair of sub-carriers.

In accordance with an aspect of the present invention, there is providedan electronic wireless communication apparatus for including a pluralityof demodulation reference signal (DMRS) symbols in a physical resourceblock format in a communication system, the apparatus comprisingcircuitry configured to: convert input data into modulation symbols, theconverting comprising performing Pi/2 binary phase shift keying (BPSK)modulation on the input data; and transmit a combination of themodulation symbols and the plurality of DMRS symbols using a pair ofsub-carriers of the physical resource block format, wherein subsequentones of the plurality of DMRS symbols are alternatingly transmitted ondifferent ones of the pair of sub-carriers.

In accordance with another aspect of the present invention, there isprovided a method for implementing a cyclic prefix in 2 sub-carrier Pi/2binary phase shift keying modulation in a communication system, themethod comprising applying phase rotations to modulation symbolstransmitted on two different sub-carriers, such that the phase rotationsapplied to modulation symbols transmitted on a first sub-carrier are thesame as the phase rotations applied to modulation symbols transmitted ona second sub-carrier. The same phase rotations can be generated based atleast in part on an average frequency of the two sub-carriers, which maybe adjacent sub-carriers in a PRB, and which may be the only twosub-carriers used at a given time by a transmitting apparatus. That is,additional sub-carriers of the PRB may be unused (by the present methodand apparatus) for transmission.

In accordance with another aspect of the present invention, there isprovided a method for transmitting symbols in a physical resource blockformat in a communication system, the method comprising: convertinginput data into modulation symbols, the converting comprising performingPi/2 binary phase shift keying (BPSK) modulation on the input data;performing a discrete Fourier transform pairwise on the modulationsymbols, or on the modulation symbols combined with additionalmodulation symbols; performing a phase rotation operation on symbolsoutput by the discrete Fourier transform; optionally performing tone (k)modulation pairwise on phase rotated symbols output by the phaserotation operation in order to map respective ones of each pair of phaserotated symbols to respective ones of the pair of sub-carriers; addingcyclic prefixes to symbols output by the tone (k) modulation (whereperformed) to generate a plurality of prefixed symbols; and transmittingthe prefixed symbols using a pair of sub-carriers of the physicalresource block format, wherein the phase rotation operation comprisesapplying a same phase rotation to pairs of symbols that will betransmitted concurrently on each one of the pair of sub-carriers.

In accordance with an aspect of the present invention, there is providedan electronic wireless communication apparatus for transmitting symbolsin a physical resource block format in a communication system, theapparatus comprising circuitry configured to: convert input data intomodulation symbols, the converting comprising performing Pi/2 binaryphase shift keying (BPSK) modulation on the input data; perform adiscrete Fourier transform pairwise on the modulation symbols, or on themodulation symbols combined with additional modulation symbols; performa phase rotation operation on symbols output by the discrete Fouriertransform; optionally perform tone (k) modulation pairwise on phaserotated symbols output by the phase rotation operation in order to maprespective ones of each pair of phase rotated symbols to respective onesof the pair of sub-carriers; add cyclic prefixes to symbols output bythe tone (k) modulation (where performed) to generate a plurality ofprefixed symbols; and transmit the prefixed symbols using a pair ofsub-carriers of the physical resource block format, wherein the phaserotation operation comprises applying a same phase rotation to pairs ofsymbols that will be transmitted concurrently on each one of the pair ofsub-carriers.

BRIEF DESCRIPTION OF THE FIGURES

These and other features of the invention will become more apparent inthe following detailed description in which reference is made to theappended drawings.

FIG. 1 illustrates DMRS transmission for legacy LTE, systems.

FIG. 2 illustrates DMRS only on I sub-carrier at a time on alternatingbetween 2 sub-carriers according to embodiments of the presentinvention.

FIG. 3 illustrates a method of inserting DMRS data before Pi/2 BPSKmodulation according to embodiments of the present invention.

FIG. 4 illustrates a method of inserting DMRS pi/2 BSPK modulatedsymbols before FFT and phase rotation of data according to embodimentsof the present invention.

FIG. 5 illustrates a method of inserting DMRS pi/2 BSPK modulatedsymbols after FFT and before phase rotation of data according toembodiments of the present invention.

FIG. 6 illustrates PAPR with the CP added to a 1 Sub-carrier Pi/2 BPSKsignal with and without phase rotation.

FIG. 7 illustrates PAPR with the CP added to a 2 Sub-carrier Pi/2 BPSKsignal, with and without NB-IoT phase rotation, according to embodimentsof the present invention.

FIG. 8 illustrates a method including using only a single phase rotationangle for both sub-carriers, according to embodiments of the presentinvention.

FIG. 9 illustrates illustrated the PAPR for the method illustrated inFIG. 8.

FIG. 10 illustrates a PAPR variation effect according to embodiments ofthe present invention.

FIG. 11 illustrates eye diagrams for forward and reverse transition forsub-carrier k=0 when PAPR is good, according to embodiments of thepresent invention.

FIG. 12 illustrates eye diagrams for forward and reverse transition forsub-carrier k-14 when PAPR is bad, according to embodiments of thepresent invention.

FIG. 13 illustrates eye diagrams wherein the SF is optimized for eachsub-carrier to balance the PAPR for the forward and reverse transitions,according to embodiments of the present invention.

FIG. 14 illustrates SF that were determined for possible sub-carriers,according to embodiments of the present invention.

FIG. 15 illustrates the PAPR using the SF as determined according toFIG. 14.

FIG. 16 illustrates an apparatus provided according an embodiment of tothe present invention.

DETAILED DESCRIPTION

Embodiments of the present invention provide methods and apparatuses forimplementation of demodulation reference signal symbols (DMRS) in 2sub-carrier Pi/2 binary phase shift keying (BPSK) modulation in acommunication system.

Embodiments of the present invention provide methods and apparatuses forimplementation of symbol phase rotations and cyclic prefixes, in 2sub-carrier Pi/2 binary phase shift keying (BPSK) modulation in acommunication system.

Pi/2 BPSK modulation is described for example in U.S. Patent ApplicationNo. 62/586,432, which is incorporated herein by reference. Pi/2 BPSKmodulation, DMRS insertion, phase rotations and cyclic prefixes are alsodescribed in the 3^(rd) Generation Partnership Project (3GPP) documentnumbered 36.211, version 15.4.0, and entitled Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical channels and modulation,which is incorporated herein by reference and referred to herein as TS36.211.

The DMRS (Demodulation Reference Signal) facilitates coherentdemodulation associated with transmission of data on a physical uplinkshared channel (PUSCH). DMRS is transmitted in the fourth single-carrierfrequency division multiple access (SC-FDMA) symbol of the slot and isthe same size as the assigned resource (i.e. sent on symbol 3 and 10 ofevery SF). An example is illustrated in FIG. 1. For legacy Long-termEvolution (LTE) and for Narrowband Internet of Things (NB-IoT) when thenumber of subcarriers is greater than one, the DMRS is a type ofZadoff-Chu (ZC) Sequence. A problem is that if a ZC is used for the DMRSfor the 2 subcarrier Pi/2 BPSK modulation then the peak to average powerratio (PAPR) for those DMRS symbols may not be in a desirable range. Thepresence of such DMRS symbols may degrade the PAPR benefit derived fromusing 2 sub-carrier Pi/2 binary phase shift keying (BPSK) modulation.

Referring to FIG. 1, DMRS symbols are included at locations 110 of anLTE subframe 100 comprising a pair of physical resource blocks (PRBs)105 a, 105 b. The subframe 100 is formed of multiple resource elementsconveyed via different subcarriers (vertical axis) and different OFDMsymbols occurring, sequentially in time (horizontal axis).

According, to embodiments of the present invention, the DMRS symbols arePi/2. BPSK modulated. Pi/2 phase rotation of the DMRS is synchronizedwith data (i.e. the alternating pi/2 phase shift is maintained).Furthermore, the DMRS is transmitted on only 1 sub-carrier at a time,with such transmission alternating between the 2 sub-carriers. Anexample is illustrated in FIG. 2.

Referring to FIG. 2, portions of three consecutive subframes 205 a, 205b, 205 c are shown. As in FIG. 1, DMRS 210 are transmitted using thefourth OFDM symbols of each PRB, which correspond to the numberedsymbols 3 and 10 in FIG. 2. The symbol numbers count, from 0 to 14, theconsecutive (in time) OFDM symbols of the current subframe. Furthermore,the tone used to transmit DMRS is alternated between tone k and tonek+1. That is, for the first PRB of each subframe, tone k is used totransmit DMRS (in symbol 3) and tone k+1 is unused. For the second PRBof each subframe, tone k+1 is used to transmit DMRS (in symbol 10) andtone k is unused. Notably, both tones k and k+1 are also used for otherpurposes, such as transmitting uplink data and SRS.

For greater clarity, tone k and tone k+1 can be mapped to two differentsub-carriers of the subframes and PRBs. The two sub-carriers may beadjacent to one another and may be the only two sub-carriers presentlyused by a given apparatus for transmission. For LTE and similar systems,the sub-carriers may have 15 kHz bandwidth, with a full PRB composed ofabout 12 sub-carriers. However, in certain applications, such as the 2sub-carrier BPSK, a given uplink or downlink transmission does notnecessarily use all sub-carriers. As such, modulation symbolsrepresenting data are transmitted using a pair of tones k and k+1 atOFDM symbols 0 to 2. 4 to 9 and 11 to 12, with the two tones mapped totwo sub-carriers of the PRB format. In combination with this, DMRSsymbols are transmitted using the same pair of tones k and k+1 at OFDMsymbols 4 and 10, with the tones mapped to the same sub-carriers.Further, subsequent ones of the plurality of DMRS symbols arealternatingly transmitted on different ones of the pair of sub-carriers.That is, first, third, etc. DMRS symbols are transmitted via onesub-carrier (corresponding to tone k), whereas second, fourth, etc. DMRSsymbols are transmitted via the other sub-carrier (corresponding to tonek+1).

In various embodiments, and as shown in FIG. 2, when one of the pair ofsub-carriers is used to transmit one of the plurality of DMRS symbols,the other one of the pair of sub-carriers is unused for transmittinganother one of the plurality of DMRS symbols. In various embodiments,and as shown in FIG. 2, when one of the pair of sub-carriers is used totransmit one of the plurality of DMRS symbols, the other one of the pairof sub-carriers is unused for transmission.

According to embodiments, even though the DMRS is sent ½ as often persubcarrier (because tone k+1 is unused when tone k is used for DMRS andvice-versa), the PSD of the DMRS can be double so the channel estimateand the DMRS for tone k can be used for tone k+1 and visa-versa and thusthe resulting block error rate (BLER) performance should be similar toif not better, for lower Doppler rates. At higher Doppler rates, therecould be a minor reduction in performance but this should be very smallas the subcarriers are adjacent (i.e. only 15 kHz apart) and frequencyselective fading at less than 15 kHz (i.e. coherent bandwidth) isuncommon for indoor environments. The two-subcarrier modulationoptimization is designed for use cases of extended coverage (i.e. highMCL) caused mainly by in-building penetration where mobility beyondpedestrian is very unlikely. Given the DMRS are still sent at afrequency of about 1 kHz (once per SF) per sub-carrier. Doppler rates of200 Hz (i.e. 72 km/H at 1.5 GHz carrier frequency) are not expected tosee any significant degradation in BLER performance. In general, thecoherent bandwidth is about equal to 1/(delay spread) so as long as thedelay spread is <50 microseconds ( 1/30 kHz) little to no degradation isexpected. For indoor and micro-cellular channels, the delay spreadrarely exceeds a few hundred nanoseconds. Even for in macro-cellularchannels beyond S microseconds is considered unusual in presentapplications. For this reason, the LTE downlink pilots (CRS) are sent,in various embodiments, only once every 3 sub-carriers.

According to embodiments, there are several methods which can beimplemented in order to provide the above solution. This solution maygenerally comprise transmitting a combination of modulation symbols andDMRS symbols using a pair of sub-carriers of a physical resource blockformat, where subsequent ones of the plurality of DMRS symbols arealternatingly transmitted on different ones of the pair of sub-carriers.More particularly, in various embodiments, only two sub-carriers areused at a time for transmission, thus only using two out of twelvesub-carriers of a PRB format at a time. The two sub-carriers may beadjacent to each other. For example, when two out of a possible threecontiguous) sub-carriers are usable for transmission, two adjacent onesof the sub-carriers are selected and used for transmission. First,second and third implementation methods are discussed below.

According to some embodiments, the first implementation method includesinserting DMRS data before Pi/2 BPSK modulation. DMRS data is encoded toensure that the DMRS symbols are transmitted on alternatingsub-carriers.

FIG. 3 illustrates the first implementation method according to someembodiments. An input data stream 300 is input to a de-multiplexer 305which produces two data streams. A DMRS source 307 produces DMRS datasequences for each tone. The DMRS data sequences may be provided asbinary data, and may be referred to as DMRS symbol precursor data.Interleavers (multiplexers) 310 combine the outputs of thede-multiplexer 305 with the DMRS data sequences in a manner that willresult in the DMRS symbols being disposed at appropriate locations(symbol locations 3 and 10 as in FIG. 2) in the subsequent transmittedsubframes. In other words, the precursor data is configured andintroduced so that subsequent modulation thereof, including the Pi/2BPSK modulation, results in the resultant DMRS symbols being presentedfor alternating transmission on different ones of the pair ofsub-carriers. The interleavers create interleaved data.

The output of the interleavers 310 is provided to a modulator 315 whichperforms Pi/2 BPSK modulation on the interleaved data. Two bits may bemodulated at a time (i.e. in parallel) to produce two symbols accordingto BPSK symbol constellation(s). The BPSK symbol constellation(s) may berotated by ±Pi/2 radians after conversion of each pair of bits. Each oneof the pair of bits may be modulated using a same BPSK symbolconstellation, or different ones of the pair of bits may be modulatedusing different (e.g. rotated by Pi/2 radians relative to one another)BPSK symbol constellations.

Pairs of symbols output by the modulator 315 are subject to a FFT (orDFT) operation 320. The operation 320 outputs a pair of symbols whichcorresponds to a discrete Fourier transform of the input symbols. Pairsof symbols output by operation 320 may be subject (e.g. pairwise) to aphase rotation operation 325. The phase rotation operation may be asdescribed elsewhere herein. Generally, the phase rotation operation mayadjust the phase of modulation symbols by a given amount. In someembodiments, both symbols of each pair are subjected to the same amountof phase rotation, which may be generated based on an average frequencyof the two sub-carriers subsequently used for their transmission. Thesub-carriers are selected in the operation 330 below, and data from theoperation 330 may be fed back to the operation 325.

Pairs of symbols output of the phase rotation operation 325 (whenpresent) are subject to a Tone (k) modulation operation 330. Theoperation 330 may comprise sub-carrier mapping, in which tones k and k+1are mapped to two (typically adjacent) sub-carrier frequencies of thePRB configuration. The operation 330 may be fixed and inherent in thedefinition of the tones. The operation 330 may be configurable andperformed on generalized tones. The operation 330 may map respectiveones of each pair of phase rotated symbols to respective ones of thepair of sub-carriers. The operation 330 may map one symbol of an inputpair of symbols to a particular sub-carrier, and maps the other symbolof the input pair to another sub-carrier. The mapping is performedaccording to a predetermined mapping rule.

A cyclic prefix operation 335 may add cyclic prefixes to symbols outputof the Tone (k) modulation operation 330. Alternatively, cyclic prefixescan be added in another manner. Other operations (not shown) can also beperformed, as would be readily understood by the worker skilled in theart, such as digital-to-analog conversion, transmit filtering (e.g.Nyquist reconstruction), radiofrequency (RF) upconversion, additionalfiltering of harmonics, and power amplification.

For the first implementation, the DMRS data sequence R(n,k) needs to beencoded to make sure the DMRS output symbols a_(k,1) and a_(k+1,1) arealternating sub-carriers. If R(n,k)=R(n,k+1) then subcarrier a_(k,1)will transmitted—this is because FFT (X, X)=[2X 0]. If R(n,k)=−R(n,k+1)then subcarrier a_(k+1,1) will be transmitted—this is because FFT (X,−X)=[0 2X]. For example, the following method could be used to ensurealternating DMRS output symbols:

$\begin{matrix}\begin{matrix}{{R\left( {n,k} \right)} = {{w(n)}\left( {1 - {2{c(n)}}} \right)}} & {{k\mspace{14mu} {is}\mspace{14mu} {even}}} \\{= {{w(n)}\left( {1 - {2{c(n)}}} \right)}} & {{{k\mspace{14mu} {is}\mspace{14mu} {odd}},{n\mspace{14mu} {is}\mspace{14mu} {even}}}} \\{= {{- {w(n)}}\left( {1 - {2{c(n)}}} \right)}} & {{{k\mspace{14mu} {is}\mspace{14mu} {odd}},{n\mspace{14mu} {is}\mspace{14mu} {odd}}}}\end{matrix} & (1) \\{{Or}\text{:}} & \; \\\begin{matrix}{{R\left( {n,k} \right)} = {{w(n)}\left( {1 - {2{c(n)}}} \right)}} & {{k\mspace{14mu} {is}\mspace{14mu} {even}}} \\{= {{w(n)}\left( {1 - {2{c(n)}}} \right)}} & {{{k\mspace{14mu} {is}\mspace{14mu} {odd}},{n\mspace{14mu} {is}\mspace{14mu} {odd}}}} \\{= {{- {w(n)}}\left( {1 - {2{c(n)}}} \right)}} & {{{k\mspace{14mu} {is}\mspace{14mu} {odd}},{n\mspace{14mu} {is}\mspace{14mu} {even}}}}\end{matrix} & (2)\end{matrix}$

in the first implementation, R(n,k) denotes binary precursor data thatis used to generate appropriate DMRS symbols. Element k is an index oversub-carriers or tones. Element n is an index over bits in the DMRS datasequence. Element 1 is an index over symbols, and bits n are mapped tosymbols 1 via modulation (e.g. with successive bits mapped to successivesymbols). Further, in the above, w represents a Hadamard code havingelements w(n), and c represents a Gold sequence having elements c(n).However, w and c may represent other, substantially equivalent values.

According to embodiments, to obtain orthogonal patterns, a similarconcatenated Hadamard code w(n) and Gold sequence c(n) could he used(same as single sub-carrier for NB-IoT).

According to embodiments, a potential advantage of the firstimplementation method is that the Pi/2 phase shift is done in one placeso synchronization of the pi/2 phase shift is easy. For example, asingle component can be used to modulate both input data and the DMRSdata sequence.

According to some embodiments, the second implementation method includesinserting DMRS Pi/2 BSPK modulated symbols before FFT and phase rotationof data and DMRS needs to be synchronized.

Although fast Fourier transforms (FFT) are used in the presentdescription, it should be noted that the FFT may be replaced withanother type of discrete Fourier transform (DFT). The Fourier transformcan be implemented numerically, using appropriately configuredcircuitry, or via an equivalent operation such as a look-up table, aswould be readily understood by a worker skilled in the art.

FIG. 4 illustrates the second implementation method in accordance tosome embodiments of the present invention. FIG. 4 includes many of thesame components as FIG. 3, but in a different order. Further, DMRSsource 307 is replaced with DMRS source 407 which produces DMRS symbolsrather than precursor data. The interleavers 310 are placed after thePi/2 BPSK modulator 315 and interleave the BPSK modulated symbols withthe DMRS symbols to produce interleaved output. Output of theinterleavers 310 is provided to the FFT operation 320. Therefore, incontrast with FIG. 3, interleaving is performed after BPSK modulation,and appropriate DMRS symbols are interleaved with the data symbols in amanner which causes the DMRS symbols to be transmitted by theappropriate tone (e.g. alternating between tones k and k+1) at theappropriate time (e.g. at symbol locations 3 and 10 in a givensubframe). The DMRS symbols are generated so that subsequent handlingthereof results in the plurality of DMRS symbols being presented foralternating transmission on the different ones of the pair ofsub-carriers. The DMRS symbols may be generated such that theinterleaved output comprises a consistent pattern of alternating Pi/2phase shifts between successive symbols. As illustrated, the subsequenthandling may include some or all of: performing a FFT operation 320 (orother discrete Fourier transform) on the interleaved output; performinga phase rotation operation 325 on output of the discrete Fouriertransform; and performing tone (k) modulation 330 pairwise on phaserotated symbols output by the phase rotation operation, in order to maprespective ones of each pair of phase rotated symbols to respective onesof the pair of sub-carriers.

In the second implementation, the DMRS sequence R(n,k) is encoded in amanner which causes the output a_(k,1) and a_(k+1,1) to be alternating,(In the second and third implementation, R(n,k) denotes symbols, ratherthan precursor binary data). Based on the subsequent operations, it ispossible to generate such a DMRS sequence. For example, for followingmethod could be used:

$\begin{matrix}\begin{matrix}{{R\left( {n,k} \right)} = {{\overset{\_}{r}}_{u}(n)}} & {{k\mspace{14mu} {is}\mspace{14mu} {even}}} \\{= {{\overset{\_}{r}}_{u}(n)}} & {{{k\mspace{14mu} {is}\mspace{14mu} {odd}},{n\mspace{14mu} {is}\mspace{14mu} {even}}}} \\{= {- {{\overset{\_}{r}}_{u}(n)}}} & {{{k\mspace{14mu} {is}\mspace{14mu} {odd}},{n\mspace{14mu} {is}\mspace{14mu} {odd}}}}\end{matrix} & (3)\end{matrix}$

Where r _(u)(n) is the same as in 1 subcarrier NB-IoT:

$\begin{matrix}{{{{\overset{\_}{r}}_{u}(n)} = {\frac{1}{\sqrt{2}}\left( {1 + j} \right)\left( {1 - {2{c(n)}}} \right){w\left( {n\; {mod16}} \right)}}},{0 \leq n < {M_{rep}^{NPUSCH}N_{slots}^{UL}N_{RU}}}} & (4)\end{matrix}$

According to embodiments, to get orthogonal patterns, a similarconcatenated Hadamard code w(n) and Gold sequence c(n) can be used (sameas 1 sub-carrier for NB-IoT).

According to embodiments, the Pi/2 phase shifts are done in two placeswhich need to be coordinated to make sure the final sequence has analternating pi/2 phase shift. The two places correspond to phase shiftsapplied when modulating the input data, and phase shifts applied whengenerating the DMRS. For example, if the initial data at symbol 0 is notPi/2 rotated, then the DMRS at symbol 3 should be Pi/2 rotated but theDMRS sent at symbol 10 should not be Pi/2 rotated.

According to some embodiments, the third implementation method includesinserting DMRS Pi/2 BSPK modulated symbols after FFT, and for examplebefore phase rotation of data. Furthermore, Pi/2 phase rotation of boththe data and the DMRS may be synchronized. The synchronization is suchthat the Pi/2 phase rotation characteristic of Pi/2 BPSK is present insubstantially the same form in the symbol stream comprising bothmodulated data symbols and DMRS.

FIG. 5 illustrates the third implementation method in accordance to someembodiments of the present invention. FIG. 5 includes many of the samecomponents as FIGS. 3 and 4, but in a different order. Further, DMRSsource 307, 407 is replaced with DMRS source 507 which produces DMRSsymbols. The interleavers 310 are placed after the FFT transformer 320and interleave the BPSK modulated and FFT transformed symbols with theDMRS symbols to produce interleaved output. Output of the interleavers310 is provided to the phase rotation operation 325, if present.Therefore, in contrast with FIGS. 3 and 4, interleaving is performedafter FFT, and appropriate DMRS symbols are interleaved with theFFT-transformed data symbols in a manner which causes the DMRS symbolsto be transmitted by the appropriate tone (e.g. alternating betweentones k and k+1) at the appropriate time (e.g. at symbol locations 3 and10 in a given subframe).

The DMRS symbols are generated (and interleaved) so that subsequenthandling thereof results in the plurality of DMRS symbols beingpresented for alternating transmission on said different ones of thepair of sub-carriers. As illustrated, the subsequent handling caninclude, for example, one or both of: performing a phase rotationoperation on the interleaved output; and performing tone (k) modulationpairwise on phase rotated symbols output by the phase rotation operationin order to map respective ones of each pair of phase rotated symbols torespective ones of the pair of sub-carriers.

In the third implementation, the DMRS symbol sequence A(n,k)) mayfurther be encoded to cause the outputs a_(k,1) and a_(k+1,1) to bealternating. In other words, DMRS symbols are generated so that, aftersubsequent handling, the DMRS symbols are presented for alternatingtransmission on the two different sub-carriers. For example, forfollowing method could be used:

$\begin{matrix}\begin{matrix}{{A\left( {n,k} \right)} = {2^{*}{{\overset{\_}{r}}_{u}(n)}}} & {{{k\mspace{14mu} {is}\mspace{14mu} {even}},{n\mspace{14mu} {is}\mspace{14mu} {odd}}}} \\{= 0} & {{{k\mspace{14mu} {is}\mspace{14mu} {even}},{n\mspace{14mu} {is}\mspace{14mu} {even}}}} \\{= 0} & {{{k\mspace{14mu} {is}\mspace{14mu} {odd}},{n\mspace{14mu} {is}\mspace{14mu} {odd}}}} \\{= {2^{*}{{\overset{\_}{r}}_{u}(n)}}} & {{{k\mspace{14mu} {is}\mspace{14mu} {odd}},{n\mspace{14mu} {is}\mspace{14mu} {even}}}}\end{matrix} & (5)\end{matrix}$

Where r _(u)(n) is the same as in 1 subcarrier NB-IoT modulation.

According to embodiments, in this method the Pi/2 phase shifts are donein two separate blocks which may be coordinated together. For example,if the initial data at symbol 0 is not rotated, then the DMRS at symbol3 should be Pi/2 rotated but the DMRS sent at symbol 10 should not bePi/2 rotated.

Embodiments of the present invention further provide methods andapparatuses for implementation of cyclic prefix (CP) in 2 sub-carrierPi/2 binary phase shift keying (BPSK) modulation in a communicationsystem.

In a situation including a sequence of symbols to be transmitted oneafter the other without a cyclic prefix (CP), the transitions from onesymbol to the next would always have a phase discontinuity of plus orminus Pi/2. SC-FDMA as used in LTE requires a CP of a fixed length. Thisresults in a phase shift between the end of the CP and the start of thenext symbol that is not necessarily plus or minus Pi/2. The additionalphase rotation depends on the frequency of the modulated tone, the phaseshift at the symbol boundary is no longer always Pi/2. The actualresulting phase change can be between 0 and Pi. A transition of Pitransits the center of the complex plane, resulting in a larger powervariation than a Pi/2 transition which causes an increase in PAPR. Theincrease in the PAPR may be more significantly affected by anyexcursions of power above the average. This happens when the digitallymodulated signal is filtered, as is required in practical implementationto avoid generating sampling images in other Nyquist zones that willinterfere with adjacent channels. The amount of overshoot of thetrajectory of the filtered signal beyond its average raises the peak ofthe signal amplitude which defines a higher PAPR.

If the amount of the phase change between the end of the CP and thestart of the next symbol can be known, an additional phase rotation canbe introduced to correct the phase change to be Pi/2, or much closer toit. A scheme for doing so is a part of the NB-IoT standard for 1sub-carrier Pi/2. BPSK, for example as described in Section 10.5.1 of TS36.211.

FIG. 6. Illustrates variation of PAPR (vertical axis) over each of 12sub-carriers (horizontal axis) of a PRB, according to an illustrativeexample. Curve 610 illustrates variation of PAPR with the CP added to a1 sub-carrier Pi/2 BPSK signal with the above-mentioned NB-IoT phaserotation. Curve 620 illustrates variation of PAPR with the CP added to a1 sub-carrier Pi/2 BPSK signal, and without the above-mentioned NB-IoTphase rotation. As seen from FIG. 6, the phase rotation improves thePAPR for all 12 Sub-carriers of a PRB.

A similar issue occurs for eMTC with 2 sub-carrier Pi/2 BPSK. Also, incurrent implementations, eMTC needs to support 72 subcarriers over awider 1.08 MHz bandwidth. FIG. 7 shows the PAPR (vertical axis) with theCP included, with and without the above NB-IoT phase rotation, over 72subcarriers (horizontal axis). As illustrated in FIG. 7, the PAPR 720without any phase rotation adjustment is shown, along with the PAPR 710resulting from using the same phase rotation approach as NB-IoT. Thisshows that the NB-IoT approach is not beneficial, or only of marginalbenefit. This is because with the eMTC in-phase Pi/2 BPSK, the tones areat different frequencies so the phase rotation needed to reduce PAPRdepends on which tone is transmitted.

According to embodiments, the additional phase rotation would bedependent on the tone that was transmitted, for example:

if Lower tone sent

-   -   phi+=2*pi*ToneSpace*(k+0.5)*CPLengthSamples/SamplingRate;

else Upper tone sent

-   -   phi+=2*pi*ToneSpace*(k+1.5)*CPLengthSamples/SamplingRate;

end

Here, Lower tone and. Upper tone refer to the two tones/subcarriers kand k+1, respectively. The term phi+ refers to the additional phaserotation, ToneSpace refers to the frequency spacing between tones, krefers to a particular subcarrier index, CPLengthSamples refers to thecyclic prefix length samples and SamplingRate refers to the samplingrate.

However, since this is data dependent it is not immediately evident howthe reciever could know a priori which tone is to be transmitted.Therefore decoding is not practical. As such, methods and apparatusesare required which can provide good PAPR when CP is included for 2 tonein-phase Pi/2 BPSK.

According to embodiments of the present invention, there is provided amethod for implementing cyclic prefixes in a communication system suchas LTE or eMTC. The method includes using only a single phase rotationangle for both sub-carriers (in contrast to current NB-IoTimplementations which involve only one sub-carrier). The method includesrotating phase based on the average (e.g. mean) frequency of bothsub-carriers.

According to embodiments of the present invention, using the averagefrequency is not expected to necessarily give perfect Pi/2 transitionsat the symbol boundaries but because the two sub-carriers are adjacent,the transitions are much closer to pi/2 than if no phase adjustments aremade.

FIG. 8 illustrates this method and associated apparatus in accordance tosome embodiments of the present invention. It is noted that FIG. 8 canbe combined with FIG. 3, 4 or 5, in order to interleave DMRS symbols orprecursor data with the binary data or symbols representing same.According to FIG. 8 An input data stream 800 is input to ade-multiplexer 805 which produces two data streams. The two streams canbe operated on pairwise (in parallel on a symbol-by-symbol basis) insubsequent operations.

The output of the demultiplexer 805 is provided to a modulator 815 whichperforms BPSK modulation, thus converting input data into modulationsymbols. As previously mentioned, two bits may be modulated at a time(i.e. in parallel) to produce two symbols according to BPSK symbolconstellation(s). The BPSK symbol constellation(s) may be rotated by±Pi/2 radians after conversion of each pair of bits. Each one of thepair of bits may be modulated using a same BPSK symbol constellation, ordifferent ones of the pair of bits may be modulated using different(e.g. rotated by Pi/2 radians relative to one another) BPSK symbolconstellations.

Pairs of symbols output by the modulator 815 are subject to a FFT (orDFT) operation 820. The operation 820 outputs a pair of symbols whichcorresponds to a discrete Fourier transform of the input symbols. Pairsof symbols output by operation 820 may be subject to a phase rotationoperation 825. The phase rotation operation performs phase rotations onpairs of symbols in the manner described herein. For example, the samephase rotation can be applied to each one of each pair of symbols thatwill be transmitted concurrently on each one of the pair ofsub-carriers. The phase rotation operates on pairs of symbols inparallel (i.e. the pairs of symbols output by FFT operation 820). Thesame phase rotation is applied to each of these pairs of symbolsoperated on in parallel, that is, on pairs of symbols which will betransmitted concurrently on different ones of the pairs of sub-carriers.The phase rotation can incorporate other aspects. For example, the phaserotation can be generated based on an average frequency of the pair ofsubcarriers subsequently used. A scaling factor may be applied todetermine the phase rotations.

Pairs of symbols output of the phase rotation operation 825 are subjectto a Tone (k) modulation operation 830. The operation 830 is performedpairwise on phase rotated symbols output by the phase rotation operationin order to map respective ones of each pair of phase rotated symbols torespective ones of the pair of sub-carriers. The operation 830 maycomprise sub-carrier mapping, in which tones k and k+1 are mapped to two(typically adjacent) sub-carrier frequencies of the PRB configuration.The operation 830 may be fixed and inherent in the definition of thetones. The operation 830 may be configurable and performed ongeneralized tones. The operation 830 may map respective ones of eachpair of phase rotated symbols to respective ones of the pair ofsub-carriers. The operation 830 may map one symbol of an input pair ofsymbols to a particular sub-carrier, and maps the other symbol of theinput pair to another sub-carrier. The mapping is performed according toa predetermined mapping rule.

A cyclic prefix operation 835 may add cyclic prefixes to symbols outputof the Tone (k) modulation operation 830. This generates prefixedsymbols, as will be readily understood by a worker skilled in the art.Alternatively, cyclic prefixes can be added in another manner. Otheroperations (not shown) can also be performed, as would be readilyunderstood by the worker skilled in the art, such as digital-to-analogconversion, transmit filtering (e.g. Nyquist reconstruction),radiofrequency (RF) upconversion, additional filtering of harmonics, andpower amplification. The prefixed symbols are subsequently transmittedusing a pair of sub-carriers of the PRB format.

According to embodiments, the method can be defined mathematically asfollows:

-   -   For N_(sc) ^(RU)=2 (i.e. 2 tone), the time-continuous signal        s_(k,l)(t) for two tone index k in SC-FDMA symbol l is defined        by:

$\begin{matrix}{{S_{k,l}(t)} = {{a_{k,l} \cdot e^{j\; \varphi_{k,l}} \cdot e^{j\; 2{\pi {({k + {1/2}})}}{{\Delta f}{({t - {N_{{CP},l}T_{s}}})}}}} + {a_{{k + 1},l} \cdot e^{j\; \varphi_{k,l}} \cdot e^{j\; 2{\pi {({k + {3/2}})}}{{\Delta f}{({t - {N_{{CP},l}T_{s}}})}}}}}} & (6)\end{matrix}$

For 0≤t<(N_(CP)+N)T_(s), where Δf=15 kHz, T_(s)=30720000 is samplingfrequency, N_(CP) is cycle prefix length, N=2048, k=−36: 35, a_(k,l) isthe content of resource element (k,1) (i.e. which is the pi/2 BPSK 2ptFFT modulation value of symbol l for the lower tone—see FIG. 8 anda_(k+1,1) is the content of resource element (k+1,1) (i.e. resourceelement of upper tone) and the phase rotation ϕ_(k,l) is defined by

$\begin{matrix}{\varphi_{k,l} = \left\{ \begin{matrix}0 & {l = 0} \\{{\phi_{k}\left( {l - 1} \right)} + {2{{{\pi\Delta}f}\left( {k + 1} \right)}N_{CP}T_{s}}} & {l > 0}\end{matrix} \right.} & (7)\end{matrix}$

where l is a symbol counter that is reset at the start of a transmissionand incremented for each symbol during the transmission. According tosome embodiments, the term “(k+1)” in the above phase rotation equationrepresents the average of the lower tone (k+1/2) and upper tone (k+3/2).Thus, the phase rotation of each of two tones subcarriers) is the same,and each update is based on the average frequency of the two tones(subcarriers). It should be readily understood that Equation (7) abovecan be varied in sonic ways. For example, the term N_(CP) can bereplaced with (N+N_(CP)).

As shown by Equation (7) above, the same phase rotation for a currentpair of symbols may be derived in part based on the same phase rotationfor an immediately prior pair of symbols plus an offset incorporatingthe average frequency of the pair of sub-carriers.

FIG. 9 illustrates the PAPR (vertical axis) for the above method. ThePAPR is plotted for 72 different tones (horizontal axis). As seen fromabove, the “new” (i.e., as proposed herein) phase rotation is animprovement over the NB-IoT method especially for the centersub-carriers (or Tone #'s). In more detail, curve 910 illustrates PAPRwhere phase rotation is applied as proposed in the prior NB-IoT method.Curve 920 illustrates PAPR without phase rotation. Curve 930 illustratesPAPR where phase rotation is applied in accordance with an embodiment ofthe present invention.

According to embodiments, user equipment (UE) implementation-basedimprovements can include re-tuning center frequency and including ascaling factor within an updating term for recursively generating aphase rotation value.

According to embodiments, for sub-carriers farther from the centerfrequency (f_(c)), the PAPR generally increases. This is due to thetransmit filter or reconstruction filter effects. A half duplexfrequency division duplexing (HD-FDD) eMTC UE has a 1 msreceive-transmit (RX-TX) re-tune gap which provides enough time for theUE to re-tune its local oscillator (i.e. f_(c)) to avoid these negativePAPR affects of the transmit filter to allow for generating the tonepair at the center of this plot. However, if frequency hopping withinthe 1.08 MHz bandwidth in FI)D is used then this technique may not bepossible as there would likely not be enough time to re-tune the localoscillator between hops.

According to embodiments, as seen from FIG. 9, the PAPR is worse for thesub-carriers away from the center. Given that the sample rate may be1.92 MHz, a filter that cuts off at 3 MHz does not sufficiently suppresssampling images in adjacent frequencies. As seen in FIG. 10, this PAPRvariation effect is more pronounced when the transmit filter cut-off isreduced to a more practical 800 KHz from 3 MHz. The increase in PAPR isdue to the fact that the +pi/2 transitions (i.e. forward transition) donot have the same PAPR as the −pi/2 transition (i.e. reverse transition)due to the transmit filtering affects. In more detail. FIG. 10illustrates the PAPR (vertical axis), plotted for 72 different tones(horizontal axis). Curve 1010 illustrates PAPR without phase rotation.Curve 1020 illustrates PAPR where phase rotation is applied inaccordance with an embodiment of the present invention, and with atransmit filter cut-off frequency of 800 kHz. Curve 1030 illustratesPAPR where phase rotation is applied in accordance with an embodiment ofthe present invention, and with a transmit filter cut-off frequency of 3MHz.

In more detail, the pi/2 BPSK modulation on its own advances or retardsthe phase. Without the addition of the cyclic prefixes, these phasetransitions occur on the symbol boundaries. Filtering is performed tomitigate sudden discontinuities or jumps in waveforms at these symbolboundaries. The cyclic prefix extends the symbol by adding additionalrotation that substantially randomizes the finishing phase of one symbolrelative to the beginning of the next symbol. Embodiments of the presentinvention mitigate this unpredictable and potentially detrimental phasediscontinuity by resetting it to a more consistently lower phasediscontinuity.

FIG. 11 illustrates the eye diagrams for forward (1110) and reverse(1120) transitions for sub-carrier k=0 where PAPR is good. Thissub-carrier is far below the filter cut-off and the PAPR is fairlysimilar for both transitions.

FIG. 12 illustrates the eye diagrams for forward (1210) and reverse(1220) transition for sub-carrier k=14 where PAPR is bad. Thissub-carrier is close to the filter cut-off. We see that the PAPR isdifferent for both transitions and the resulting PAPR will have a highernumber. In particular, the forward transition results in biggerexcursions above the average than the reverse transition which causesmost of the increased PAPR.

In more detail, PAPR can be undesirably bad due to larger than apredetermined amount of amplitude variation, which contributes to thePAPR. Ideally there would be no such variation, so lower amplitudevariation is considered better. Short transitions outside (above) theaverage circle (referring to the eye diagrams) can be particularlyproblematic because ideally the amplifier should be operated with itspeak output close to its average output. If this is achieved and then asignal significantly above the average is input to the amplifier,clipping and hence signal distortion can occur. Embodiments of thepresent invention can be implemented to mitigate such a situation.

According to embodiments, a solution to this problem is to add a scalingfactor (SF) to the equation phase rotation equation defined below.

$\begin{matrix}{\varphi_{k,l} = \left\{ \begin{matrix}0 & {l = 0} \\{{\phi_{k}\left( {l - 1} \right)} + {{SF}^{*}2{{{\pi\Delta}f}\left( {k + 1} \right)}N_{{CP},l}T_{s}}} & {l > 0}\end{matrix} \right.} & (8)\end{matrix}$

As seen in Equation (8), the current phase rotation is derived from aprior phase rotation plus an offset term, where the offset term ismultiplied by a scaling factor SF. The SF changes the phase rotation tobalance the PAPR for the forward and reverse transitions. The SF maydepend on characteristics of the transmit filter used in transmittingthe prefixed symbols. The UE may be configured to determine a-priori aSF for each subcarrier index k to use, based on the transmit filter itwill use. As mentioned, one possible method to optimize the SF for eachsub-carrier is to balance the PAPR for the forward and reversetransitions. Using this approach with a 800 kHz transmit filter, ascaling factor of 0.86 was determinded for subcarrier k=14 where the eyediagrams for forward (1310) and reverse (1320) transitions areillustrated (with scaling factor applied) in FIG. 13. Where the PAPR isreduced from 1.08 to 0.55 dB. The resulting phase changes between theend of the CP and the start of the next symbol when applying the SF willnot typically be + or −Pi/2. The scaling factor may thus be configuredto balance a peak-to-average power ratio for forward and reverse phasetransitions.

According to embodiments, using the above approach with the 800 kHzfilter, the SFs determined for all possible sub-carriers, are asillustrated in FIG. 14. The PAPR using the scaling factors defined inFIG. 14 (as well as phase rotation) is the bottom curve 1530 illustratedin FIG. 15. For comparison, the PAPR using phase rotation but no scalingfactor is shown as curve 1520, and the PAPR without phase rotation isshown as curve 1510. The vertical axis is PAPR, and the horizontal axisshows the 72 tones. As seen from the above, using a scaling factor toadjust the phase rotation can improve the PAPR for the worst casesub-carriers with very little degradation for the best.

According to embodiments, although the base station may not necessarilyknow what scaling factor the UE will use, as long as the scaling factoris small the base station may see this as a small phase error. The phaseerror will only be on the CP portion since the scaling factor (SF) isapplied only to the CP and the CP is typically ˜6.6% (4.7 us of 71 us).For example, if SF=0.8 then the total phase error is (1−0.8)*7.6%=1.3%which would only cause a very small degradation in detection or BLERperformance.

According to embodiments, there is provided methods and apparatuses foran OFDMA system, SC-FDMA, 2 sub-carrier pi/2 BPSK with cyclic prefixadded wherein phase rotation is used to compensate for CP rotation.According to some embodiments, the same phase rotation is applied toboth sub-carriers. According to some embodiments phase rotation is basedon the average frequency of the two sub-carriers.

According to some embodiments, the transmitter may retune the localoscillator (i.e. f_(c)) if the transmitted sub-carrier is too close tothe cut-off of the transmit (or reconstruction) filter. For example, thetransmitter may be configured to determine if a frequency of one of thepair of sub-carriers is within a predetermined range of a cut-offfrequency of a transmit filter used in transmission of the prefixedsymbols or reconstruction filter involved in reception of the prefixedsymbols. When the frequency is within the predetermined range, thetransmitter may re-tune a local oscillator generating frequencies of thesub-carriers.

According to some embodiments, the methods include applying asub-carrier dependent scaling factor to the phase rotation. In someembodiments, the scaling factor can be determined a-priori based on theeffects of transmit filters. In some embodiments, the scaling factor canbe determined a-priori by equalizing the PAPR for the forward andreverse phase transitions.

Embodiments of the present invention can be used for wireless (i.e.radio) communication in an OFDMA communication system, for exampleoperating according to the LTE standard. Embodiments of the presentinvention can be used for communication in an SC-FDMA system, forexample operating according to the LTE standard. Embodiments of thepresent invention comprise signal modulation using a two-tone Sub-PRBscheme, as described above. Embodiments of the present invention furthercomprise signal modulation using a pi/2 BPSK scheme, in conjunction withthe two-tone scheme. Embodiments of the present invention furthercomprise this two-tone pi/2 BPSK signal modulation in the in-phasemanner as described above.

It should be noted that embodiments of the present invention can bevaried in several ways. For example, performing a discrete Fouriertransform pairwise on modulation symbols can be combined with thepreceding modulation operation by causing the modulation operation tomap input data to symbols in a manner that, in a single step, producesthe same output symbols as the two-step Pi/2 BPSK modulation followed bythe discrete Fourier transform operation. Other operations can besimilarly combined. Some operations can be omitted when not required.For example, phase rotation can be omitted in some embodiments whichinvolve alternatingly transmitting DMRS symbols on different ones of apair of sub-carriers. As another example, an explicit tone (k)modulation operation can be omitted if the two tones are always mappedto the same pair of sub-carriers, in which case the pairs of symbolsoutput e.g. from phase rotation or discrete Fourier transform may beprovided directly for use in modulating the pair of sub-carriers.

Embodiments of the present invention provide for a method fortransmitting data, for example wirelessly, using a modulation scheme asdescribed above. The method can be implemented on an electronic devicehaving wireless communication capability. The device can include atleast a source of data to be transmitted, an antenna, and electronicsfor generating the modulated signal for transmission by the antennabased on the sourced data. The electronics can be in the form of anapplication specific integrated circuit, field programmable gate array,signal processor, microcontroller, processor coupled to memory, or thelike, or a combination thereof.

Embodiments of the present invention provide for an apparatus fortransmitting data, for example wirelessly, using a modulation scheme asdescribed above. The apparatus can be an electronic device such as thatdescribed above, or a portion thereof, such as an electronic componenthaving the described functionality.

Embodiments of the present invention provide for a method and apparatusfor receiving and processing data transmitted in the manner describedabove. The method can be implemented on, and the apparatus can be, anelectronic device having wireless communication to ability, as describedabove, or a portion of such an electronic device.

FIG. 16 illustrates an apparatus provided according an embodiment of thepresent invention. The apparatus includes a source of data 1610, abaseband processor 1615, transmit circuitry 1620, receive circuitry1625, and an antenna 1630. The source of data 1610 a baseband processor1615, transmit circuitry 1620 and receive circuitry 1625 can be providedusing various electronic components, including baseband (e.g. processor,FPGA, ASIC, etc.) and/or RE components, as would be readily understoodby a worker skilled in the art.

It will be appreciated that, although specific embodiments of thetechnology have been described herein for purposes of illustration,various modifications may be made without departing from the spirit andscope of the technology. In particular, it is within the scope of thetechnology to provide a computer program product or program element, ora program storage or memory device such as a magnetic or optical wire,tape or disc, or the like, for storing signals readable by a machine,for controlling the operation of a computer according to the method ofthe technology and/or to structure some or all of its components inaccordance with the system of the technology.

Acts associated with the method described herein can be implemented ascoded instructions in a computer program product. In other words, thecomputer program product is a computer-readable medium upon whichsoftware code is recorded to execute the method when the computerprogram product is loaded into memory and executed on the microprocessorof the wireless communication device.

Acts associated with the method described herein can be implemented ascoded instructions in plural computer program products. For example, afirst portion of the method may be performed using one computing device,and a second portion of the method may be performed using anothercomputing device, server, or the like. In this case, each computerprogram product is a computer-readable medium upon which software codeis recorded to execute appropriate portions of the method when acomputer program product is loaded into memory and executed on themicroprocessor of a computing device.

Further, each step of the method may be executed on a computing device,such as a personal computer, server, PDA, or the like and pursuant toone or more, or a part of one or more, program elements, modules orobjects generated from any programming language, such as C++, Java, orthe like. In addition, each step, or a file or object or the likeimplementing each said step, may be executed by special purpose hardwareor a circuit module designed for that purpose.

It is obvious that the foregoing embodiments of the invention areexamples and can be varied in many ways. Such present or futurevariations are not to be regarded as a departure from the scope of theinvention, and all such modifications as would be obvious to one skilledin the art are intended to be included within the scope of the followingclaims.

We claim:
 1. A method for including a plurality of demodulationreference signal (DMRS) symbols in a physical resource block format in acommunication system, the method comprising: converting input data intomodulation symbols, the converting comprising performing Pi/2 binaryphase shift keying (BPSK) modulation on the input data; and transmittinga combination of the modulation symbols and the plurality of DMRSsymbols using a pair of sub-carriers of the physical resource blockformat, wherein subsequent ones of the plurality of DMRS symbols arealternatingly transmitted on different ones of the pair of sub-carriers.2. The method of claim 1, wherein when one of the pair of sub-carriersis used to transmit one of the plurality of DMRS symbols, the other oneof the pair of sub-carriers is unused for transmitting another one ofthe plurality of DMRS symbols.
 3. The method of claim 1, wherein whenone of the pair of sub-carriers is used to transmit one of the pluralityof DMRS symbols, the other one of the pair of sub-carriers is unused fortransmission.
 4. The method of claim 1, wherein the converting furthercomprises: performing a discrete Fourier transform pairwise on symbolsgenerated by the Pi/2 BPSK modulation; performing a phase rotationoperation pairwise on symbols output by the discrete Fourier transform;and performing tone (k) modulation pairwise on phase rotated symbolsoutput by the phase rotation operation in order to map respective onesof each pair of phase rotated symbols to respective ones of the pair ofsub-carriers.
 5. The method of claim 1, further comprising creating thecombination of the modulation symbols and the plurality of DMRS symbolsby: generating DMRS symbol precursor data; interleaving the input datawith the DMRS symbol precursor data to create interleaved data; andperforming the Pi/2 BPSK modulation on the interleaved data, wherein theDMRS symbol precursor data is configured so that subsequent modulationthereof, including the Pi/2 BPSK modulation, results in the plurality ofDMRS symbols being presented for alternating transmission on saiddifferent ones of the pair of sub-carriers.
 6. The method of claim 5,wherein the DMRS symbol precursor data is given by a plurality of bitsR(n,k), where n is an index over bits, k is an index over tones beingmapped to sub-carriers, and: $\begin{matrix}{{R\left( {n,k} \right)} = {{w(n)}\left( {1 - {2{c(n)}}} \right)}} & {{k\mspace{14mu} {is}\mspace{14mu} {even}}} \\{= {{w(n)}\left( {1 - {2{c(n)}}} \right)}} & {{{k\mspace{14mu} {is}\mspace{14mu} {odd}},{n\mspace{14mu} {is}\mspace{14mu} {even}}}} \\{= {{- {w(n)}}\left( {1 - {2{c(n)}}} \right)}} & {{{k\mspace{14mu} {is}\mspace{14mu} {odd}},{n\mspace{14mu} {is}\mspace{14mu} {odd}}}}\end{matrix}$ or: $\begin{matrix}{{R\left( {n,k} \right)} = {{w(n)}\left( {1 - {2{c(n)}}} \right)}} & {{k\mspace{14mu} {is}\mspace{14mu} {even}}} \\{= {{w(n)}\left( {1 - {2{c(n)}}} \right)}} & {{{k\mspace{14mu} {is}\mspace{14mu} {odd}},{n\mspace{14mu} {is}\mspace{14mu} {odd}}}} \\{= {{- {w(n)}}\left( {1 - {2{c(n)}}} \right)}} & {{{k\mspace{14mu} {is}\mspace{14mu} {odd}},{n\mspace{14mu} {is}\mspace{14mu} {even}},}}\end{matrix}$ wherein w(n) is a bit of a Hadamard code sequence and c(n)is a bit of a Gold code sequence.
 7. The method of claim 1, furthercomprising creating the combination of the modulation symbols and theplurality DMRS symbols by: generating the DMRS symbols; interleavingsymbols output by the Pi/2 BPSK modulation with the DMRS symbols toproduce interleaved output, wherein the DMRS symbols are generated sothat subsequent handling thereof results in the plurality of DMRSsymbols being presented for alternating transmission on said differentones of the pair of sub-carriers.
 8. The method of claim 7, wherein saidsubsequent handling comprises some or all of: performing a discreteFourier transform on the interleaved output; performing a phase rotationoperation on output of the discrete Fourier transform; and performingtone (k) modulation pairwise on phase rotated symbols output by thephase rotation operation in order to map respective ones of each pair ofphase rotated symbols to respective ones of the pair of sub-carriers. 9.The method of claim 7, wherein the DMRS symbols are further generatedsuch that the interleaved output comprises a consistent pattern ofalternating Pi/2 phase shifts between successive symbols thereof. 10.The method of claim 1, wherein the converting further comprisesperforming a discrete Fourier transform pairwise on symbols generated bythe Pi/2 BPSK modulation, the method further comprising creating thecombination of the modulation symbols and the plurality of DMRS symbolsby: generating the DMRS symbols; and interleaving symbols output of thediscrete Fourier transform with the DMRS symbols to produce interleavedoutput, wherein the DMRS symbols are generated so that subsequenthandling thereof results in the plurality of DMRS symbols beingpresented for alternating transmission on said different ones of thepair of sub-carriers.
 11. The method of claim 10, wherein saidsubsequent handling comprises one or both of: performing a phaserotation operation on the interleaved output; and performing tone (k)modulation pairwise on phase rotated symbols output by the phaserotation operation in order to map respective ones of each pair of phaserotated symbols to respective ones of the pair of sub-carriers.
 12. Themethod of claim 1, wherein the physical resource block format comprisesthe pair of sub-carriers as well as additional sub-carriers, and whereinthe additional sub-carriers are unused for transmission.
 13. The methodof claim 1, wherein the pair of sub-carriers are adjacent to one anotherin the physical resource block format.
 14. An electronic wirelesscommunication apparatus for including a plurality of demodulationreference signal (DMRS) symbols in a physical resource block format in acommunication system, the apparatus comprising circuitry configured to:convert input data into modulation symbols, the converting comprisingperforming Pi/2 binary phase shift keying (BPSK) modulation on the inputdata; and transmit a combination of the modulation symbols and theplurality of DMRS symbols using a pair of sub-carriers of the physicalresource block format, wherein subsequent ones of the plurality of DMRSsymbols are alternatingly transmitted on different ones of the pair ofsub-carriers,
 15. The apparatus of claim 14, wherein when one of thepair of sub-carriers is used to transmit one of the plurality of DMRSsymbols, the other one of the pair of sub-carriers is unused fortransmitting another one of the plurality of DMRS symbols.
 16. Theapparatus of claim 14, wherein when one of the pair of sub-carriers isused to transmit one of the plurality of DMRS symbols, the other one ofthe pair of sub-carriers is unused for transmission.
 17. The apparatusof claim 14, wherein the converting further comprises: performing adiscrete Fourier transform pairwise on symbols generated by the Pi/2BPSK modulation; performing a phase rotation operation pairwise onsymbols output by the discrete Fourier transform; and performing tone(k) modulation pairwise on phase rotated symbols output by the phaserotation operation in order to map respective ones of each pair of phaserotated symbols to respective ones of the pair of sub-carriers.
 18. Theapparatus of claim 1, the circuitry further configured to create thecombination of the modulation symbols and the plurality of DMRS symbolsby: generating DMRS symbol precursor data; interleaving the input datawith the DMRS symbol precursor data to create interleaved data; andperforming the Pi/2 BPSK modulation on the interleaved data, wherein theDMRS symbol precursor data is configured so that subsequent modulationthereof, including the Pi/2 BPSK modulation, results in the plurality ofDMRS symbols being presented for alternating transmission on saiddifferent ones of the pair of sub-carriers.
 19. The apparatus of claim18, wherein the DMRS symbol precursor data is given by a plurality ofbits R(n,k), where n is an index over bits, k is an index over tonesbeing mapped to sub-carriers, and: $\begin{matrix}{{R\left( {n,k} \right)} = {{w(n)}\left( {1 - {2{c(n)}}} \right)}} & {{k\mspace{14mu} {is}\mspace{14mu} {even}}} \\{= {{w(n)}\left( {1 - {2{c(n)}}} \right)}} & {{{k\mspace{14mu} {is}\mspace{14mu} {odd}},{n\mspace{14mu} {is}\mspace{14mu} {even}}}} \\{= {{- {w(n)}}\left( {1 - {2{c(n)}}} \right)}} & {{{k\mspace{14mu} {is}\mspace{14mu} {odd}},{n\mspace{14mu} {is}\mspace{14mu} {odd}}}}\end{matrix}$ or: $\begin{matrix}{{R\left( {n,k} \right)} = {{w(n)}\left( {1 - {2{c(n)}}} \right)}} & {{k\mspace{14mu} {is}\mspace{14mu} {even}}} \\{= {{w(n)}\left( {1 - {2{c(n)}}} \right)}} & {{{k\mspace{14mu} {is}\mspace{14mu} {odd}},{n\mspace{14mu} {is}\mspace{14mu} {odd}}}} \\{= {{- {w(n)}}\left( {1 - {2{c(n)}}} \right)}} & {{{k\mspace{14mu} {is}\mspace{14mu} {odd}},{n\mspace{14mu} {is}\mspace{14mu} {even}},}}\end{matrix}$ wherein w(n) is a bit of a Hadamard code sequence and c(n)is a bit of a Gold code sequence.
 20. The apparatus of claim 14, thecircuitry further configured to create the combination of the modulationsymbols and the plurality DMRS symbols by: generating the DMRS symbols;interleaving symbols output by the Pi/2 BPSK modulation with the DMRSsymbols to produce interleaved output, wherein the DMRS symbols aregenerated so that subsequent handling thereof results in the pluralityof DMRS symbols being presented for alternating transmission on saiddifferent ones of the pair of sub-carriers.
 21. The apparatus of claim20, wherein said subsequent handling comprises some or all of:performing a discrete Fourier transform on the interleaved output;performing a phase rotation operation on output of the discrete Fouriertransform; and performing tone (k) modulation pairwise on phase rotatedsymbols output by the phase rotation operation in order to maprespective ones of each pair of phase rotated symbols to respective onesof the pair of sub-carriers.
 22. The apparatus of claim 20, wherein theDMRS symbols are further generated such that the interleaved outputcomprises a consistent pattern of alternating Pi/2 phase shifts betweensuccessive symbols thereof.
 23. The apparatus of claim 14, wherein theconverting further comprises performing a discrete Fourier transformpairwise on symbols generated by the Pi/2 BPSK modulation, the methodfurther comprising creating the combination of the modulation symbolsand the plurality of DMRS symbols by: generating the DMRS symbols; andinterleaving symbols output of the discrete Fourier transform with theDMRS symbols to produce interleaved output, wherein the DMRS symbols aregenerated so that subsequent handling thereof results in the pluralityof DMRS symbols being presented for alternating transmission on saiddifferent ones of the pair of sub-carriers.
 24. The apparatus of claim23, wherein said subsequent handling comprises one or both of:performing a phase rotation operation on the interleaved output; andperforming tone (k) modulation pairwise on phase rotated symbols outputby the phase rotation operation in order to map respective ones of eachpair of phase rotated symbols to respective ones of the pair ofsub-carriers.
 25. The apparatus of claim 14, wherein the physicalresource block format comprises the pair of sub-carriers as well asadditional sub-carriers, and wherein the additional sub-carriers areunused for transmission.
 26. The apparatus of claim 14, wherein the pairof sub-carriers are adjacent to one another in the physical resourceblock format.